1. Field of the Invention
The present invention relates generally to condensation polymers. It relates in particular to polyimides containing pendent ethynyl groups. It relates also in particular to diamines containing pendent ethynyl groups, which diamines are used in the preparation of the polyimides containing pendent ethynyl groups.
2. Description of Related Art
Polyimides are condensation polymers that can be prepared by various synthetic routes. The most popular route involves the reaction of an aromatic dianhydride with an aromatic diamine. The intermediate polyamide acid is either thermally or chemically cyclodehydrated to form the polyimide, which has a repeat unit of the general type ##STR1## where Ar is a tetravalent aromatic radical, which can be as simple as a 1,2,4,5-tetrasubstituted benzene. Alternatively, Ar may be a bis-4(1,2-methylenediphenylene) having the general structure ##STR2## where X=nil, O, S, SO.sub.2, C.dbd.O, etc. Moreover, Ar may be any other appropriate tetravalent radical. Ar' is a divalent aromatic radical which may be 1,3=phenylene, 1,4-phenylene, 4,4'-oxydiphenylene, 4,4'-biphenylene, 4,4'-thiodiphenylene, 4,4'-carbonyldiphenylene, diphenyimethane or any other appropriate divalent radical.
Synthesis and characterization of polyimides has been extensively reported in the literature. The preparation of aromatic polyimides by reaction of an aromatic dianhydride with an aromatic diamine, followed by thermal cyclization was first reported in 1963 (G. M. Bower and L. W. Frost, J. Polym. Sci. A1, 3134 (1963)) with patents awarded in 1965 (W. M. Edwards, U.S. Pat. Nos. 3,179,614 and 3,179,634 and A. L. Endrey, U.S. Pat. Nos. 2,1796,631 and 3,179,633). Several reviews on polyimides have been published (C. E. Sroog, "Polyimides" in Encycl. of Polymr. Sci. and Tech. [H. F. Mark, N. G. Gaylord and N. M. Bikales, ed.] Interscience Pub., New York, 1969, Vol. 11, pp. 247-272; N. A. Adrova, M. I. Bessonov, L. A. Lauis and A. P. Rudakov, Polyimides, Technomic Pub. Co., Inc., Stamford, Conn., 1970).
Wholly aromatic polyimides are known for their exceptional thermal, thermooxididative and chemical resistance, but are generally difficult to process as structural adhesives or composite matrices. Several polyimides such as Kapton.RTM. (DuPont), PI-2080 (Dow Chemical), XU-218 (Ciba-Geigy), Ultem.RTM. (General Electric) and LaRC.TM.-TPI (Mitsui Toatsu) are commercially available and used as films, moldings, adhesives or composite matrices.
The incorporation of ethynyl groups in polyimides has been reported in the literature, typically as terminal groups to yield acetylene-terminated imide oligomers (ATI). Therimid-600, an oligomide with acetylenic end groups, was first developed at the Hughes Aircraft Co. [N. Bilow, A. L. Landis and L. J. Miler, U.S. Pat. No. 3,845,018 (1974); A. L. Landis, N. Bilow, R. H. Boschan, R. E. Lawrence and T. J. Aponyi, Polym. Prepr., 15, 537 (1974); N. Bilow and A. L. Landis, Natl. SAMPE Tech. Conf. Ser., 8,94 (1976)]. Several reviews on polyimides or acetylene-terminated prepolymers are published which discuss other acetylene containing polyimides [P. M. Hergenrother (H. Mark, ed.), Encycl. Polym. Sci. and Eng., 2nd. ed., Vol. 1, John Wiley and Sons, Inc., New York, 61 (1985); P. M. Hergenrother (H. Mark, ed.) Encycl. Polym Sci. and Eng., 2nd ed., Vol. 7, John Wiley and Sons, Inc., New York, 639 (1987); T. Takekoshi (C. G. Overberger, ed.) Advances in Polymer Sci., 2 ( 1990)]. Polyimides containing pendent ethynyl groups has been reported [F. W. Harris, S. M. Podaki and S. Varaprath, Polym. Prepr., 21 (1), 3 (1980)]. This reference contains an abstract only, no experimental details or polymer properties being reported.